1. Field of the Invention
The invention relates to optical devices and more particularly to protecting image sensor during die handling.
2. Description of Related Art
Digital imaging systems, such as for example digital cameras, utilize integrated circuit devices or chips as image capturing devices. An imaging system, such as a camera, uses light to capture an image on a semiconductor-based chip. The chip replaces film in traditional film-based systems. In a digital camera, an image sensor is configured, in its simplest form, to capture a monochrome or color image by way of field effect transistors (FETs), such as complementary metal oxide semiconductor (CMOS) devices or charge coupled devices (CCDs).
In one example, the image sensor is a semiconductor chip made up of a number of photosensitive circuits, each photosensitive circuit capable of absorbing light. In color applications, each photosensitive circuit generally absorbs light through a color filter that represents a particular wavelength of light in the visible spectrum corresponding to the image sensed.
The photosensitive circuits of an image sensor, often referred to as pixel circuits, are generally arranged in an array such as for example 480 rows by 640 columns. In general, each photosensitive circuit or pixel circuit contains a photosensitive element, such as a photodiode, and other circuitry. The photosensitive element defines a photosensing region or area of the photosensitive circuit that responds to light while the circuitry, generally speaking, drives a light signal from the photosensitive region or area to other process circuitry. Typically the image sensor is surrounded at its edges by bond pads that electrically connect the image sensor to the other components of the imaging system.
The CMOS- or CCD-based image sensor is formed as a chip or die of a wafer of a number of chips and dies. Once formed, the wafer is divided into individual chips or dies using conventional wafer dividing tools. The individual chips or dies are then removed from the processing station by a die handler such as a collet. During the die handling process, there is a possibility of damaging the individual dies or chips. The damage translates to unit losses.
Prior efforts to minimize the unit losses encountered by die or chip handling processes include placing a scratch protection layer outside the photosensitive region or area of the chip that is resistant to damage during the die or chip handling process. One method involves placing color filter array (CFA) material outside the photosensitive region or area to act as a scratch protection layer. The primary use of CFA material is over the photosensitive region or area to absorb light according to a particular wavelength of the visible spectrum, allowing the image sensor to interpret color images.
CFA material is typically a photo-imageable material such as an acrylic resin with a pigment or die. The material is coated on a wafer, baked, and exposed to ultraviolet light through a mask to crosslink or polymerize the CFA material where desired. The remainder of the CFA material is then removed. One problem with CFA material is incomplete crosslinking. Incomplete crosslinking leads to defects in the CFA material. One way to reduce the number of defects caused by incomplete crosslinking is to minimize the area covered by CFA material. Thus, prior art efforts that use CFA material as a scratch protection layer increase the area of usage on the image sensor of CFA material and therefore increase the defect count of the CFA material.
Thus, what is needed is a suitable scratch protection material to minimize unit losses that does not increase the defect count of CFA material on a sensor.
An optical device is disclosed. The optical device includes a semiconductor-based substrate having a photosensitive circuit including a photosensitive area a portion of which is covered by color filter array material, a contact area surrounding the photosensitive area, and a microlens material overlying the portion of the photosensitive area and a portion of a contact area.